Go and play GTAV's last mission from the start...you can't...yet it's an open world game. How would MGS as an open world change the story? Give me examples.
First you rescue Donald Anderson, it's the players choice on how to get to him, but he will always be in the same place and the cutscene would be exactly the same. Next is Baker, again in the same place, where you fight Ocelot and have the same cutscene...
The structure of Shadow Moses might change, but the information that is passed on wouldn't.
Simple, what would be the point of having an open world with nothing to do in it and we still have to follow the same path to the same people to the same end goal?
It wouldn't make sense.
Would Kojima keep the layout of the Shadow Moses Facility the same?
If it was an open world then maybe it'd make more sense to have the whole archipelago open to the player and spread the facility over multiple islands?
I admit the story COULD stay relatively the same but more than likely it'd change to include a bigger Foxhound unit with more Bosses considering the player space would have become a lot bigger.
This alone changes the story, even if kojima was to simply move a Boss to a different location this would also change the story as we knew it.
There would likely be more codec conversations because to be honest it'd be boring if we had to cross multiple islands without the colonel mumbling in our ear.
Kojima would have to add into the story the retcons and back storystory he added in with peace walker MGS3.
This would change the story.
Why are we even having this discussion? Kojima has said already that he'd keep the best bits and completely start anew.
And next time add in a real open world structured game like assassin's creed or something sandbox like hitman.